1. Field of the Invention
The present invention relates to a sound generating device of an electronic keyboard instrument that includes a speaker unit having a tweeter and a woofer.
2. Description of the Related Art
Conventionally, there has been known a sound generating device of an electronic keyboard instrument where a multi-way speaker system is used. For example, Japanese Patent Publication No. 2541017 discloses a keyboard instrument having a tweeter and a main speaker (i.e., a woofer) disposed on a speaker box so as to both be directed upwardly and adjacent to each other, with the speaker box mounted on a main body of the keyboard instrument.
In a sound generating device of this type, a musical tone signal is usually band-divided into signals for the tweeter and the woofer. However, there is overlap (so-called crossover frequency) between frequencies allocated by the band division to the tweeter and the woofer, as described in “Hi-Fi Speaker and Full Use Thereof” Beginner's Radio, Stereo Technic Soft & Hard, separate volume, Seibundo Shinkosha Co., Ltd., pp. 193 to 205, Jul. 10, 1968.
In most cases, the keyboard instrument audience are on a lateral side of the keyboard instrument and at a height level nearly equal to the main body of the keyboard instrument. On the other hand, in the keyboard instrument disclosed in Japanese Patent Publication No. 2541017, both the tweeter and the woofer are directed upwardly and disposed at different positions in the horizontal direction. Accordingly, depending on listening points, i.e., the positions of the audience, a distance from the tweeter to each listening point slightly differ from a distance from the woofer to the listening point. As a result, due to sound wave interference, a problem is posed that acoustic characteristic runaway (variation, dip, etc.) takes place in a frequency range where there is overlap between frequencies allocated to the tweeter and the woofer (see, FIG. 15 in Japanese Patent Publication No. 2541017).